Ultrafine polyamide fiber, and melt-spinning method and device therefor

ABSTRACT

Ultrafine polyamide fiber includes polyamide fiber with a single yarn fineness of 0.10 dtex or more and 0.50 dtex or less and an average number of 1.0 or less per 12,000 m of a filament in a length direction.

TECHNICAL FIELD

This disclosure relates to ultrafine polyamide fiber with a very smallsingle yarn fineness, and more specifically relates to ultrafinepolyamide fiber that serves to impart high softness, smoothness, drapeproperty, high water absorption capacity, high density, and highpost-dyeing quality to woven or knitted fabrics.

BACKGROUND

Having a wide range of good characteristics including mechanicalcharacteristics, polyamide fibers have been widely used for productionof clothing and industrial materials. Among other clothing materials,false-twisted yarns have been in wide use for products such as wovenfabrics and knitted fabrics, and have been manufactured in largequantities. In particular, ultrafine false-twisted yarns with a singleyarn fineness of 1.2 dtex or less can produce cloth having very softtexture as well as improved heat retaining and water absorptioncapacities compared with false-twisted yarns with common levels ofsingle yarn fineness. Accordingly, ultrafine false-twisted yarns havebeen in increased demands and now dominate the market.

For these applications of ultrafine polyamide fibers, there is aproposal of ultrafine polyamide fiber intended for false-twisting thatcan impart softness to cloth as a result of being produced fromultrafine polyamide fiber for false-twisting containing fiber ofpolyamide resin with a single yarn fineness of 1.2 dtex or less andhaving specially specified friction coefficient, elongation percentage,and hot water shrinkage rate (Japanese Unexamined Patent Publication(Kokai) No. 2005-320655).

There is another proposal of polyamide fiber for false twisting usefulto produce false-twisted crimped threads with high softness that isproduced from polyamide fiber having a single yarn fineness of 1.2 dtexor less and also having a specially specified stress at 15% elongationand opening length of interlaced portions (Japanese Unexamined PatentPublication (Kokai) No. 2009-084749).

A proposed method of applying a finishing oil uniformly to theseultrafine polyamide fibers is to cool single yarns uniformly by aso-called “ring chimney,” which is an apparatus designed so that polymerthreads discharged from a spinning spinneret with discharge holesarranged along a ring are cooled by applying cool air in all directionsalong their inner or outer circumferences, and subsequently apply afinishing oil from oil guides located opposite to each other with theyarns interposed in between (Japanese Unexamined Patent Publication(Kokai) No. 2007-126759).

There is another proposed method in which a finishing oil is supplieduniformly to single yarns on the downstream side of a spinning spinneretprovided with a plurality of discharge holes arranged along a ring, bybringing the single yarns into contact with a plate located inside theplurality of filaments discharged from discharge holes (JapaneseUnexamined Patent Publication (Kokai) No. 2010-126846).

However, if an attempt is made to produce still thinner ultrafinepolyamide fiber with a fineness of 0.5 dtex or less by a method asdescribed in JP '655 and JP '749, it is difficult to achieve uniformcooling or uniform lubrication and result in ultrafine polyamide fibersuffering from large Uster unevenness and poor fuzzing quality.Furthermore, as a result of larger differences in fiber structure amongsingle yarns, breakage of yarns and a decrease in reelability of yarnswill take place when subjected to false twisting, or significant fuzzingwill take place during warping when subjected to weaving or knitting,thus leading to disadvantages such as decreased smoothness and qualityin cloth production and significant uneven dyeing in dyed cloth.

If applied to solving this problem, the finishing oil supply methoddescribed in JP '759 will have to bundle the yarns while supplying afinishing oil. Ultrafine polyamide fibers with a single yarn fineness of0.5 dtex or less have peculiar disadvantages that the strength of eachsingle yarn decreases, that the single yarns rub each other during thebundling of yarns, and that the fiber before finishing oil supply has alarge friction coefficient. Accordingly, the rubbing between singleyarns and the rubbing between single yarns and the guides that takeplace before finishing oil supply will cause breakage of single yarns,prevent the finishing oil from being applied uniformly to single yarnsin the inner portions of bundled yarns, cause differences in the amountof the finishing oil and water attached to single yarns, and causedifferences in fiber structure among single yarns, thereby leading todyed yarns with inferior quality.

If an attempt is made to apply the method described in JP '846, uniformfinishing oil supply is difficult in the length direction of the fiber,although the single yarns can be lubricated uniformly. Furthermore,uneven adhesion of the finishing oil will take place in the lengthdirection, leading to differences in fiber structure and a variation infriction coefficient in the length direction. Thus, there remaindisadvantages that a variation in tension occurs in the length directiondue to rubbing with yarn guides during the spinning step and high orderprocessing steps, which leads to uneven dyeing in dyed yarns and failurein producing high-quality cloth.

It could therefore be helpful to provide ultrafine polyamide fiber thatimparts high softness, smoothness, drape property, high water absorptioncapacity, high density, and high post-dyeing quality to woven or knittedfabrics.

SUMMARY

We thus provide:

-   -   (1) Ultrafine polyamide fiber comprising polyamide fiber with a        single yarn fineness of 0.10 dtex or more and 0.50 dtex or less        in which filaments have an average number of fuzzes of 1.0 or        less per 12,000 m in the length direction.    -   (2) Ultrafine polyamide fiber as defined in (1) wherein the        Uster unevenness of filaments in the length direction is 1.0% or        less.    -   (3) Ultrafine polyamide fiber as defined in either (1) or (2)        having a total fineness of 15 to 300 dtex and containing 30 or        more filaments.    -   (4) Ultrafine polyamide fiber as defined in any of (1) to (3)        wherein filaments have a modified cross section.    -   (5) Ultrafine polyamide fiber as defined in any of (1) to (3)        comprising single yarns in which filaments have a circular        filament cross section, wherein the orientation parameters of        the single yarns with a circular cross section are such that the        ratio of the orientation parameter of the surface portion of the        single yarn to the orientation parameter of the central portion        of the single yarn is 1.10 or more.    -   (6) A melt-spinning method for ultrafine polyamide fiber having        a single yarn fineness of 0.10 dtex or more and 0.50 dtex or        less and having an average of 1.0 or less fuzzes per 12,000 m in        the length direction, wherein melt-spun yarns discharged from a        spinning spinneret provided with discharge holes arranged        circumferentially in the outer circumferential portion of the        spinning spinneret are cooled by a cooling apparatus located        below the central portion of the spinning spinneret and designed        to cool the melt-spun yarns by applying cooling air from either        inside or outside of the melt-spun yarns discharged from the        discharge holes, and a finishing oil is supplied by a circular        finishing oil supply apparatus having a disk-like guide portion        that is located vertically below the cooling apparatus and that        is in contact with the single yarns at its outer circumferential        portion, and also having a circular finishing oil-discharging        slit that is located directly above the guide portion and        arranged along the outer circumference of the guide, followed by        the bundling of yarns and second-stage finishing oil supply        performed simultaneously by a bundle-guide type finishing oil        supply apparatus.    -   (7) The melt-spinning method as defined in (6) wherein the        cooling apparatus is designed to cool the melt-spun yarns by        supplying cooling air from inside of the melt-spun yarns        discharged from the discharge holes.    -   (8) The melt-spinning method as defined in either (6) or (7)        wherein the cooling apparatus meets the following requirements:        -   (i) the distance (L) from the face of the spinning spinneret            to the cooling start position of the cooling apparatus is as            follows: 10 mm≦L≦70 mm, and        -   (ii) cooling air provided at the cooling start position has            a flow speed of 15 to 60 m/min.    -   (9) A melting spinning apparatus for ultrafine polyamide fiber        having a single yarn fineness of 0.10 dtex or more and 0.50 dtex        or less and having an average of 1.0 or less fuzzes per 12,000 m        in the length direction, that comprises a spinning spinneret        provided with discharge holes arranged circumferentially in the        outer circumferential portion of the spinning spinneret, and a        cooling apparatus located below the central portion of the        spinning spinneret and designed to cool the melt-spun yarns by        applying cooling air from inside or outside of the melt-spun        yarns discharged from the discharge holes, and further comprises        a circular finishing oil supply apparatus having a disk-like        guide portion that is located vertically below the cooling        apparatus and that is in contact with the single yarns at its        outer circumferential portion and also having a circular        finishing oil-discharging slit that is located directly above        the guide portion and arranged along the outer circumference of        the guide, as well as a bundle-guide type finishing oil supply        apparatus located thereunder and designed to bundle the yarns        and perform second-stage finishing oil supply simultaneously.    -   (10) The melt-spinning apparatus as defined in (9) wherein the        cooling apparatus is designed to cool the melt-spun yarns by        applying cooling air from inside of the melt-spun yarns        discharged from the discharge holes.

As described below, our ultrafine polyamide fiber produces woven orknitted fabrics with high softness, smoothness, drape property, highwater absorption capacity, high density, and high post-dyeing qualitythat cannot be realized with conventional ultrafine polyamide fibers canbe obtained using polyamide fiber that has a single yarn fineness of0.10 dtex or more and 0.50 dtex or less and has an average of 1.0 orless fuzzes per 12,000 m in the length direction. In addition, excellentanti-see-through property can also be imparted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of the ultrafine polyamidefiber production method.

FIG. 2 is a diagram illustrating a shape example of spinneret holes tobe used for production of the ultrafine polyamide fiber.

FIG. 3 is a diagram illustrating another shape example of spinneretholes to be used for production of the ultrafine polyamide fiber.

FIG. 4 is a diagram illustrating a preferred example of cyclic finishingoil supply apparatus to be used for production of the ultrafinepolyamide fiber.

FIG. 5 is a diagram illustrating another example of the ultrafinepolyamide fiber production method.

EXPLANATION OF NUMERALS

-   1. spinneret-   2. heat retaining zone under spinneret-   3. outward blow type circular cooling apparatus-   4. circular finishing oil supply apparatus-   5. bundle-guide type finishing oil supply apparatus-   6. interlacing nozzle-   7. take-up roller-   8. drawing roller-   9. winder (wind-up apparatus)-   10. fiber filament-   11. fiber product package-   12. finishing oil-discharging slit-   13. disk-like guide-   14. fiber filament-   15. finishing oil pool-   16. finishing oil discharged from slit-   17. finishing oil feed pipe-   18. inward blow type circular cooling apparatus

DETAILED DESCRIPTION

Examples of our fibers, methods and devices are described in detailbelow.

Polyamide used in the ultrafine polyamide fiber is a homopolymer or acopolymer of polyamide, and such a polyamide is a melt-moldable polymercontaining an amide bond that is formed from lactam, aminocarboxylicacid, or a salt of dicarboxylic acid with diamine.

There are no specific limitations on the polyamide to be used, andvarious useful polyamides are available, but polycaproamide (NYLON 6)and polyhexamethylene adipamide (NYLON 66) are preferable from theviewpoint of fiber-forming capability and dynamic characteristics.Usable copolymers of these polyamides such as NYLON 6 and NYLON 66include those in which other units such as aminocaproic acid and lactamaccount for 20 mol % or less of the total monomer units.

It is preferable that a polyamide has a sulfuric acid relative viscosityof 2.0 to 3.5, more preferably 2.4 to 3.0, and still more preferably 2.5to 2.7, from the viewpoint of yarn-making stability. The sulfuric acidrelative viscosity should be determined by the method described later.

In addition to the primary component, second and third components may becopolymerized with or mixed in the polymer.

In particular, the polyamide may contain polyvinyl pyrolidone ifhygroscopicity is required.

Furthermore, the polyamide may contain various additives including, forinstance, delustering agent, flame retardant, antioxidant, ultravioletabsorber, infrared ray absorbent, crystal nucleating agent, andfluorescent whitening agent, as required.

There are no specific limitations on the ultrafine polyamide fiberproduction method as long as ultrafine polyamide fiber can be obtained.However, a preferred process includes the steps of melting polyamide,discharging it from discharge holes arranged circumferentially in theouter circumferential portion of a spinning spinneret, cooling it by acooling apparatus located below the central portion of the spinneret anddesigned to cool the melt-spun yarns rapidly and uniformly by applyingcooling air from inside or outside of the melt-spun yarns dischargedfrom the discharge holes, and subsequently supplying a finishing oil toeach single yarn by a circular finishing oil supply apparatus locatedvertically below the cooling apparatus, followed by bundling of theyarns and second-stage finishing oil supply performed simultaneously bya bundle-guide type finishing oil supply apparatus. A one-process methodin which the second-stage finishing oil supply is followed by steps forinterlacing the yarns and winding them up into a package, as required,is preferred because polyamide fiber with particularly small finenessunevenness and fuzzing can be obtained and from the viewpoint of costreduction. The cooling apparatus is preferably a circular type coolingapparatus, more preferably an outward blow type circular coolingapparatus that supply cooling air from inside toward outside of the spunyarns running on circular circumferences or an inward blow type circularcooling apparatus that supply cooling air from outside toward inside ofthe spun yarns. The use of an outward blow type circular coolingapparatus is particularly preferable.

A preferable example of the polyamide fiber production method isdescribed in detail with reference to FIGS. 1 to 5. FIGS. 1 to 5 areschematic diagrams illustrating an example of the polyamide fiberproduction method. FIG. 1 gives an example that uses an outward blowtype circular cooling apparatus 3, and FIG. 5 gives an example that usesan inward blow type circular cooling apparatus 18. In the followingdescription, the production processes shown in FIG. 1 and FIG. 5 consistof basically the same constituents, and descriptions of constituentswith the same numerals are omitted.

In FIG. 1, molten polyamide is discharged through an spinneret 1 andpassed through a heat retaining zone 2 under the spinneret, andsubsequently, cooling air is applied from inside toward outside of thespun yarns by an outward blow type circular cooling apparatus 3installed below the spinneret center to reduce fineness unevenness inthe length direction, thereby rapidly cooling the single yarns at auniform distance from the spinneret face to cause their solidification.Before bundling the yarns, it is preferable that a finishing oil issupplied to each single yarn by a circular finishing oil supplyapparatus 4 having a disk-like guide portion that is in contact with thesingle yarn at the outer circumferential portion of the disk and alsohaving a finishing oil-discharging circular slit formed directly abovethe guide portion and along the outer circumference of the guide,followed by bundling of the yarns and second-stage finishing oil supplyperformed simultaneously by a bundle-guide type finishing oil supplyapparatus 5. After the finishing oil supply step, the yarns areinterlaced by an interlacing nozzle 6 as required, and wound up by awinder (wind up apparatus) 9 after passing on a take-up roller 7 and adrawing roller 8. Fiber filaments 10 and a package of the fiber product11 are also shown. Two or more sets of rollers may be used for drawingbefore winding-up into a package, but in that case, the draw ratioshould be low because the interlaced yarns can become loose as a resultof drawing, or an interlacing step may be performed again after drawing.

In the heat retaining zone 2 under the spinneret, the practice ofblowing out steam toward the spinneret face to fill the heat retainingzone 2 under the spinneret with steam is preferred because this preventsthe polymer and oligomers contained in the polymer existing around thedischarge holes of the spinneret from reacting with oxygen to solidifyand contaminate the spinneret. For this operation, it is preferable thatthe steam blow-out pressure is 0.1 to 0.5 kPa. If the blow-out pressureis too low, the oxygen concentration in the heat retaining zone underthe spinneret will be high and impair the spinneret face contaminationprevention effect, whereas if the blow-out pressure is too high, it willcause swinging of discharged yarns and lead to an increased Usterunevenness.

For cooling spun yarns arranged on circular circumferences, the use of acircular type cooling apparatus to apply radial outward cooling air tothe yarns is preferred because oligomer components formed from thepolyamide discharged from the spinneret and the steam that seals thespinneret face will be prevented from retaining inside the spinningapparatus and will be released outside.

An outward blow type circular cooling apparatus 3 is used in theproduction process shown in FIG. 1, but an inward blow type circularcooling apparatus 18 as illustrated in FIG. 5 may be used instead of theoutward blow type circular cooling apparatus 3. The inward blow typecircular cooling apparatus 18 will be installed to surround the spunyarns below the spinneret center and serve to apply cooling air fromoutside toward inside of the spun yarns, thereby rapidly cooling thesingle yarns at a uniform distance from the spinneret face to causetheir solidification.

It is preferable that the cooling start distance, that is, the distance(L) from the spinneret face to the top of the cooling air blow-outportion of the circular type cooling apparatus, is 10 to 70 mm, morepreferably 10 to 60 mm, and still more preferably 10 to 50 mm. If thecooling start distance is too short, the cooling air blown out of thecircular type cooling apparatus hits the spinneret face to lower thetemperature of the spinneret face and, accordingly, the dischargestability of the thermoplastic polymer will deteriorate, leading toincreased breakage and fuzzing of the spun yarns. If the cooling startdistance is too long, the polyamide will start to solidify before thestart of rapid, uniform cooling by cooling air and, accordingly, thefineness variation (Uster unevenness) tends to increase in the fiber'slength direction, resulting in cloth with poor quality.

It is preferable that the flow speed of the cooling air from thecircular type cooling apparatus is 15 to 60 m/min, more preferably 20 to55 m/min, and still more preferably 25 to 50 m/min. If the flow speed ofthe cooling air is too low, uniform rapid cooling of the single yarnswill not be achieved sufficiently, and the tension on the cooled yarnswill be small. Accordingly, swing of the yarns tends to be caused easilyby outside disturbances, leading to increased Uster unevenness.Furthermore, the polymer can come in contact with the guide before beingcooled adequately and, accordingly, fuzzing and breakage of spun yarnswill take place frequently, resulting in cloth with inferior quality. Ifthe flow speed of the cooling air is too high, each single yarn willsuffer from excessive tension to cause slight vibration of the yarn,leading to increased Uster unevenness and frequent yarn breakage duringspinning.

It is preferable that the temperature of the cooling air from thecircular type cooling apparatus is 5 to 50° C., more preferably 10 to40° C., and still more preferably 15 to 35° C. If the temperature of thecooling air is too low, the temperature in the heat retaining zone underthe spinneret will fall and the temperature of the spinneret face willalso fall, often leading to a decrease in the strength of the yarns,whereas if the temperature of the cooling air is too high, uniformcooling of the yarns will become difficult and the yarns will not becooled sufficiently, often leading to increased Uster unevenness andfrequent yarn breakage during spinning

It is preferable that the vertical length of the cooling air supplyportion of the circular type cooling apparatus is 100 to 500 mm, morepreferably 150 to 400 mm, and still more preferably 200 to 350 mm. Ifthe length of the cooling air supply portion is too large, each singleyarn will suffer from increased tension to cause breakage of spun yarns,whereas if the length of the cooling air supply portion is too small,the single yarns will receive a finishing oil before being cooledadequately, possibly leading to decreased fuzzing and breakage of spunyarns.

After passing the circular type cooling apparatus, the single yarns canbe subjected to treatment by a circular finishing oil supply apparatus.The circular finishing oil supply apparatus is located inside the spunyarns running on circular circumstances.

FIG. 4 is a conceptual diagram illustrating an example of a circularfinishing oil supply apparatus. This circular finishing oil supplyapparatus 4 contains a finishing oil-discharging slit 12 and a disk-likeguide 13. The circular finishing oil supply apparatus 4 is installed sothat the fiber filaments (single yarns) 14 coming from the circular typecooling apparatus are in contact with the disk-like guide 13. A circularfinishing oil-discharging slit 12 is formed along the outercircumference of the disk-like guide 13 so that a finishing oil issupplied to positions directly above the contact points of the disk-likeguide 13 with the yarns. The finishing oil is fed from a finishing oilfeed pipe 17 to a finishing oil liquid pool 15. The finishing oilfilling the finishing oil pool 15 is then discharged through thefinishing oil-discharging slit 12 and comes in contact with each singleyarn at the contact point with the yarn on the disk-like guide 13, thuslubricating each single yarn.

Bringing the single yarns coming from the circular type coolingapparatus into contact with the disk-like guide is preferred becauseswinging of the single yarns receiving cooling air is prevented anduniform cooling of the single yarns is promoted, leading to decreasedUster unevenness. Furthermore, the use of a circular finishing oilsupply apparatus that gives a finishing oil to each single yarn beforethe bundling of the yarns by discharging the finishing oil through afinishing oil-discharging circular slit that is located directly abovethe contact points of the disk-like guide with the yarns and along theouter circumference of the guide is preferred because this caneffectively prevent unlubricated yarns with high frictional resistancefrom coming in contact with the disk-like guide and depress fuzzing dueto rubbing of unlubricated single yarns with each other during thebundling of yarns, and this also serves for uniform lubrication ofsingle yarns which cannot be achieved by the finishing oil supply fromthe bundle-guide type finishing oil supply apparatus, thus preventingfuzzing due to rubbing of unlubricated single yarns with the yarn guideduring the spinning process as well as uneven dyeing during the dyeingprocess, to provide fiber suitable for high-order processing. It ispreferable that the circular finishing oil supply apparatus is locatedto supply a finishing oil at a position 300 to 1,000 mm, more preferably350 to 700 mm, and still more preferably 400 to 600 mm, from thespinneret face. If the finishing oil supply position is too high, thefinishing oil will be supplied before the single yarns have been cooledadequately, possibly causing filament strength deterioration andfuzzing, whereas if it is too low, an increased distance will berequired from the discharge of single yarns from the spinneret face totheir bundling point, and accordingly, this will cause swinging ofyarns, fuzzing, increased Uster unevenness, and increased air draggingby single yarns, leading to increased tension on running yarns andbreakage of spun yarns. There are no specific limitations on the type offinishing oil to be supplied by the circular finishing oil supplyapparatus, but it is preferable that the finishing oil is of an emulsiontype. An emulsion finishing oil can easily form a film on the guide dueto surface tension, permitting uniform finishing oil supply along thecircumference of the disk-like guide.

Adoption of a two-stage finishing oil supply consisting of finishing oilsupply by a circular finishing oil supply apparatus 4 and additionalfinishing oil supply and bundling of single yarns performedsimultaneously by a bundle-guide type finishing oil supply apparatus 5is preferred because it serves for uniform lubrication both among singleyarns and in their length direction. It is difficult for the circularfinishing oil supply apparatus 4 to obtain fibers lubricated uniformlyin the length direction although it, although the circular finishing oilsupply apparatus 4 can supply a finishing oil uniformly among singleyarns, but the two-stage finishing oil supply by the bundle-guide typefinishing oil supply apparatus 5, which provides uniform lubrication inthe length direction, and the circular finishing oil supply apparatus 4permits uniform lubrication both among single yarns and in their lengthdirection, making it possible to provide ultrafine polyamide fiber thatensures high post-dyeing quality.

The bundle-guide type finishing oil supply apparatus used for thesecond-stage lubrication may adopt a common type finishing oil supplyguide and, for instance, a finishing oil supply guide as shown in JP'759 is preferred.

It is preferable that the yarn take-up speed of the take-up roller 7 is3,500 to 4,500 m/min. If the take-up speed is too low, the orientationof the polyamide in the length direction will be unstable and unevendyeing will take place in the length direction, whereas if the take-upspeed is too high, the yarns will suffer from large tension, possiblycausing fuzzing and breakage of spun yarns. It is preferable that thedraw ratio for the drawing roller 8 is 1.0 to 1.3. If the draw ratio istoo high, the resulting fiber will be too low in elongation percentage,and in addition, breakage of single yarns will cause fuzzing easily.

The ultrafine polyamide fiber is required to have a single yarn finenessof 0.1 dtex or more and 0.5 dtex or less, preferably 0.25 to 0.45 dtex.If the fineness of the single yarns is too large, the yarns will have anexcessively high rigidity and when woven or knitted into a fabric, itwill be difficult to obtain a woven or knitted fabric with required highsoftness, smoothness, drape properties, high water absorption ability,and high density, whereas if the fineness of the single yarns is toosmall, breakage of single yarns will take place frequently during clothproduction, and the resulting cloth will tend to suffer from fuzzing andinferior smoothness as well as increased Uster unevenness, leading tocloth with inferior post-dyeing quality. The fineness of single yarnsshould be measured by the method described later.

In the ultrafine polyamide fiber, the average number of fuzzes per12,000 m of filaments in the length direction should be 1.0 or less. Anaverage number of fuzzes of larger than 1.0 will lead to fuzzing causedby warping during weaving or knitting, and breakage of threads duringfalse twisting, as well as poor reelability, and furthermore, woven orknitted fabrics produced from them will be poor in smoothness andquality. It is preferable that the average number of fuzzes per 12,000 min the length direction is 0.5 or less, more preferably 0. To reduce thenumber of fuzzes, it is preferable to prevent unlubricated single yarnswith large frictional resistance from rubbing each other and to supply afinishing oil from a circular finishing oil supply guide before bundlingof yarns. The average number of fuzzes should be measured by the methoddescribed later.

In general, fibers have a variation in yarn fineness in the lengthdirection, and thicker portions of yarns tend to be dyed more stronglyduring dyeing. In particular, this occurs more significantly in the caseof single yarns with small fineness. Fibers with large finenessunevenness will lead to woven or knitted fabrics with poor appearancedue to decreased dyeing uniformity and, therefore, it is preferable thatthe Uster unevenness (fineness unevenness) is 1.0% or less. If the Usterunevenness is too large, the yarns will suffer from a large variation insmoothness and color depth during dyeing, and products produced willtend to be poor in quality. It is preferable that the Uster unevennessis 0.9% or less. There are no specific limitations on the method to beused for decreasing the Uster unevenness, but preferable methods includerapid cooling by bringing a cooling air blow-out apparatus closer to thespinneret face, and supply of annular flow of cooling air to yarns fromouter circumference and/or inner circumference. A more preferable methodis to cool single yarns uniformly by supplying annular flow of coolingair from the inner circumference of the yarns, followed by bringing thesingle yarns in contact with a disk-like guide to prevent swinging ofthe yarns. The Uster unevenness (fineness unevenness) should be measuredby the method described later.

If the ultrafine polyamide fiber contains single yarns with a circularcross section, it is preferable that the orientation parameter of thesurface portion of those yarns and the orientation parameter of theircentral portion differ from each other. If the orientation parameterdiffers between the surface portion and the central portion, therefractive index will differ between light passing through the centralportion and that through the surface portion of the ultrafine polyamidefiber and, consequently, anti-see-through property can be developeddespite the circular cross section. Specifically, it is preferable thatthe ratio of the orientation parameter of the surface portion of asingle yarn to the orientation parameter of the central portion of thesingle yarn is 1.10 or more, more preferably 1.15 or more and 2.00 orless, and still more preferably 1.20 or more and 1.80 or less. If theratio of the orientation parameter of the surface portion of a singleyarn to the orientation parameter of its central portion is in the aboverange, light passing in the cross-sectional direction of the single yarnundergoes diffuse reflection and, therefore, cloth produced from suchsingle yarns will have anti-see-through property. In addition,excessively large strain will not occur in the internal structure of thefiber, serving to maintain adequate filament strength. The orientationparameter should be measured by the method described later. Ultrafinepolyamide fiber with such orientation parameter values can be producedunder preferred conditions as described above where the cooling startdistance is not too large while the flow speed of the cooling air(cooling air speed) is not too low.

The ultrafine polyamide fiber has a very small single yarn fineness, andfiber in which the orientation parameter structure of the surfaceportion differs from the orientation parameter structure of the centralportion can be obtained by cooling melt-spun yarns uniformly andrapidly. The ratio of the orientation parameter of the surface portionto the orientation parameter of the central portion tends to increasewhen cooling conditions serving for more rapid and uniform cooling areadopted.

Furthermore, it is preferable that this ultrafine polyamide fiber has anelongation percentage of 40 to 70%. If the elongation percentage is toolow, the tensile resistance of filaments will increase, leading to adecrease in the actual number of twists that are added by false-twistingand making it difficult to produce textured yarn with adequate crimps.In addition, drawn yarns will tend to suffer from yarn breakage andfuzzing and deteriorate in high-order passage capability. If theelongation percentage is too large, on the other hand, the actual numberof added twists will increase excessively, often resulting in texturedyarns suffering from fuzzing or a decrease in strength or drawn yarnswith a high residual elongation percentage that leads to woven orknitted fabrics suffering from streaks and deterioration in quality. Theelongation percentage should be measured by the method described later.

Furthermore, it is preferable that the stress required for 15%elongation of the resulting ultrafine polyamide fiber is 1.0 to 2.0gf/dtex (9.8×10⁻³ to 19.6×10⁻³ N/dtex), more preferably 1.2 to 1.8gf/dtex (11.8×10⁻³ to 17.6×10⁻³ N/dtex). If the stress at 15% elongationis too small, the tension caused during a false-twisting process will betoo small, often causing breakage of textured yarns, fluctuation inprocessing tension, quality deterioration of textured yarns, anddecreased yield. If the stress at 15% elongation is too large, on theother hand, a false-twisting process will cause high-degreeconcentration of tension in interlaced portions and breakage of singleyarns, leading to deterioration in process passage capability and wovenor knitted fabrics with decreased quality. The stress at 15% elongationshould be measured by the method described later.

It is preferable that the ultrafine polyamide fiber has a total finenessof 15 to 300 dtex, more preferably 15 to 200 dtex. If the total finenessis too small, the breaking strength of the fiber will be too small,leading to cloth with an excessively small tearing strength, whereas ifthe total fineness is too large, dyes will not penetrate easily into thefiber during dyeing and uneven dyeing will remain after dyeing, makingit difficult to obtain high-quality cloth. The total fineness should bemeasured by the method described later.

It is preferable that the ultrafine polyamide fiber has a filamentnumber of 30 or more, more preferably 30 to 500, still more preferably50 to 400. If the filament number is less than 30, it will be difficultto obtain an intended high softness, drape property, high waterabsorption capacity, and high density, whereas if the filament number isto large, it will lead to difficulty in uniform interlacing,deterioration in reelability, and difficulty in uniform finishing oilsupply to filaments, resulting in fuzzing attributable to breakage ofsingle yarns.

There are no specific limitations on the cross-sectional shape of theultrafine polyamide fiber, and it may have, for instance, either acircular cross section or a modified cross section. Applicable modifiedcross sections include, for instance, oblate cross section, lens-shapedcross section, trilobal cross section, hexalobal cross section,so-called “multilobal” cross section such as modified cross sectioncontaining 3 to 8 convex portions and the same number of concaveportions, hollow cross section, and other generally known modifiedcross-sections. The circular cross section is preferable from theviewpoint of spinning stability, high softness, and drape propertyimparting capability. Furthermore, if the ultrafine polyamide fiber hasa circular cross section with a preferable orientation parameter ratiobetween the central portion and the surface portion as described above,light passing in the cross-sectional direction of the single yarn willundergo diffuse reflection due to differences in orientation structure,whereas if it has a trilobal cross section, multilobal cross section, orhollow cross section, light passing through the surface undergo diffusereflection. Thus, they are preferable because cloth produced will havegood anti-see-through property due to diffuse reflection of transmittedlight. Furthermore, a trilobal cross section, a multilobal crosssection, and a mixture of filaments with a multilobal cross section andthose with a circular cross section are preferred because they serve toproduce cloth containing many gaps among single yarns, leading to largewater absorption capacity attributable to capillarity effect as well ashigh bulk density. They are also preferred because they can impartanti-see-through property attributable to diffuse reflection oftransmitted light.

The resulting ultrafine polyamide fiber produces cloth having highsoftness, smoothness, drape property, high water absorption capacity,high density, and high post-dyeing quality, as well as goodanti-see-through property in the case of a preferred example. Thus,woven fabrics produced from the ultrafine fiber is preferred as highheat-insulating lightweight material for outerwear such as down jacket.Knitted fabrics serve favorably for production of luxurious underwearhaving good functions as listed above as well as covered yarns fortights.

EXAMPLES

Our fibers, methods and devices are described in more detail below withreference to Examples.

The characteristic values used herein were determined by the followingmethods.

-   -   (1) Total Fineness and Single Yarn Fineness

Using a sizing reel with a circumference of 1.000 m, a specimen (yarn)of 27 decitex or less was wound 1,000 times and a specimen of 28 decitexor more was wound 500 times to prepare skeins, which were dried in a hotair drier at 105±2° C. for 60 min and weighed to on a balance, followedby calculating the total fineness from the measurements using thefollowing equation (i) or (ii). The total fineness thus calculated wasdivided by the number of single yarns to determine the single yarnfineness.

(i) Yarn of 27 decitex or less

Total fineness (dtex)=measured weight (g)×(10,000/1,000)×{1+(standardmoisture content (%)/100)}

(ii) Yarn of 28 decitex or more

Total fineness (dtex)=measured weight (g)×(10,000/500)×{1+(standardmoisture content (%)/100)}

For the NYLON 6 and NYLON 66 polymers used in Examples, a standardmoisture content of 4.5% was used for the fineness calculation.

Single yarn fineness (dtex)=total fineness (dtex)/number of single yarns

To determine the single yarn fineness of combined filament yarns withtwo different cross-sectional shapes (cross section A and cross sectionB), the cross section ratio of the single yarn of each cross-sectionalshape was calculated by the following equations, and the total finenessobtained above was multiplied by the cross section ratio for eithercross-sectional shape and divided by the total number of the filamentsof that shape.

Area ratio of cross section A=area of cross section A/(area of crosssection A+area of cross section B)

Area ratio of cross section B=area of cross section B/(area of crosssection A+area of cross section B)

Single yarn fineness (dtex) for cross section A in combined filamentyarns=(total fineness (dtex)×area ratio of cross section A)/number offilaments of cross section A

Single yarn fineness (dtex) for cross section B in combined filamentyarns=(total fineness (dtex)×area ratio of cross section B)/number offilaments of cross section B

(2) Sulfuric Acid Relative Viscosity

A specimen is weighed and dissolved in 98 wt % concentrated sulfuricacid to prepare a solution with a specimen concentration (C) of 1 g/100ml. It is put in an Ostwald viscometer and its falling time in seconds(T1) was measured at 25° C. Elsewhere, the falling time in seconds (T2)is measured at 25° C. for the 98 wt % concentrated sulfuric acid free ofthe specimen, and then the relative viscosity (ηr) of the specimen iscalculated by the following equation:

(ηr)=(T1/T2)+{1.891×(1.000−C)}.

(3) Average Number of Fuzzes

For determination of the average number of fuzzes, Maluti-Point FrayCounter MFC-200 (F-type sensor unit) supplied by Toray Engineering Co.,Ltd. (presently, TMT MACHINERY, INC.) was used under conditionsincluding fuzz length setting (distance from sensor light axis center toU-Guide bottom) of 2.0 mm, yarn speed of 600 m/min, and measuring timeof 20 min. After confirming that the yarn feeding tension is in therange of 0.25 g/dtex to 0.75 g/dtex, 10 measurements were made and theiraverage was taken as the average number of fuzzes (per 12,000 m).

(4) Orientation parameter ratio

The orientation parameter was measured for specimens (single yarn) witha circular cross section by Raman spectroscopy using T-64000 supplied byJobin Yvon/Atago Bussan Co., Ltd., under the following conditions:measuring mode of microscopic Raman, objective lens magnification of×100, beam diameter of 1 μm, light source of Ar⁺ laser/514.5 nm, laserpower of 100 mW, diffraction grid of Single 600, 1,800 gr/mm, slit of100 μm, and detector of CCD 1024×256 supplied by Jobin Yvon. A testsample was embedded in resin (bisphenol epoxy resin, cured for 24 hours)and cut with a microtome at a cutting angle of 5° or less from thefiber's length direction to prepare a section specimen. A sectionspecimen with a thickness of 1.5 μm was cut out so that it passesthrough the center of the fiber. Orientation was measured under twopolarized conditions: parallel polarization (∥) where the polarizingdirection is parallel with the fiber's length direction andperpendicular polarization (⊥) where they are perpendicular to eachother. The degree of orientation was evaluated based on the ratiobetween the peak strength (I₁₁₃₀) attributable to the C—C bendingvibration mode near 1130 cm⁻¹ and the peak strength (I₁₆₃₅) attributableto the C═C stretching vibration near 1635 cm⁻¹ in Raman bandmeasurements made under those conditions. Specifically, orientationparameter=(I₁₁₃₀/I₁₆₃₅)|/(I₁₁₃₀/I₁₆₃₅)⊥. Regarding the measuring points,a laser beam was applied to a point 1 μm inner from the surface portionof a single yarn for the orientation parameter of the surface portionand a point in the central portion of a single yarn for the orientationparameter of the central portion, and the measurements made were usedfor orientation parameter calculation. From the results obtained, theratio of the orientation parameter of the surface portion to theorientation parameter of the central portion was calculated by thefollowing equation. For the orientation parameters of the surface andthe central portion, five single yarns were selected at random from thefilaments and the average of their measurements was used.

Orientation parameter ratio=(orientation parameter of surface portion ofsingle yarn)/(orientation parameter of central portion of single yarn)

(5) Uster Unevenness

The Uster unevenness (½ inert, U %) was measured by using Uster TesterUT-4 supplied by Zellweger Uster under the following measuringconditions: yarn speed of 50 m/min, S-twist, twisting rate of 8,000 rpm,measuring time of 3 min.

(6) Stress at 15% Elongation

Orientec Tensiron RPC-1210A was used to measure the stress at 15%elongation. A specimen was held by clamps 50 cm apart from each otherand stretched at a tensile speed of 50 cm/min until a length of 57.5 cmwas reached, when the tension was measured. Three test runs were madeand their average was divided by the fineness of the fiber.

(7) Elongation Percentage

Orientec Tensiron RPC-1210A was used to measure the elongationpercentage. A specimen was held by clamps 50 cm apart from each otherand stretched at a tensile speed of 50 cm/min until the specimen wasbroken, when the elongation was measured. Three test runs were made andtheir average was divided by 50 cm and multiplied by 100.

(8) Softness of Cloth

Cloth was produced from the resulting fiber and dyed, and then it wassubjected to tactile and visual tests for softness, surface smoothness,drape property, and depth of the color of cloth, and evaluated accordingto the following four-rank criteria.

-   -   (A) Very good (Dyed cloth has softness, surface smoothness, and        drape property. The cloth surface is free of fuzzing.)    -   (B) Good (Good in terms of softness and drape property, but        inferior in smoothness. Part of the surface contains fuzz.)    -   (C) Slightly poor (Good in drape property, but inferior in        softness and smoothness. Part of the surface contains fuzz.)    -   (D) Poor (Cloth is stiff, and inferior in smoothness and drape        property. Surface contains fuzz.)

(9) Dyeing Quality of Cloth

The resulting fiber was used for both warp and weft to produce a plainweave fabric with a pick length of 180 cm. The cloth was dyed with anacidic dye (Mitsui Nylon Black GL). The dyed plain weave fabric wasevaluated by 10 testers using a see-through cloth inspecting machine. A100 m portion in the length direction was inspected and relativeevaluation was conducted according to the following criteria.

-   -   (A) Completely free of streaks and color depth irregularity.    -   (B) Containing slight streaks and color-depth irregularity, but        practically acceptable.    -   (C) Containing many slight streaks and color-depth irregular        portions, and practically unacceptable.    -   (D) Containing many serious streaks and color-depth irregular        portions, and practically unacceptable.

(10) Water Absorption Capacity of Cloth (Byreck Method)

Measurements were made according to JIS L1096 (1999) “Byreck Method.”Evaluation was conducted according to the following criteria based onmeasured water absorption height:

-   -   (A) 90 mm or more    -   (B) 65 mm or more and less than 90 mm    -   (C) 55 mm or more and less than 65 mm    -   (D) less than 55 mm.

(11) Anti-See-Through Property of Cloth

A tube knit fabric was produced from the resulting fiber and inspectedby 10 testers. After scouring, the anti-see-through property of thefabric was evaluated according to the following criteria:

-   -   (A) Very good (Completely free of perceived see-through        property, and acceptable as anti-see-through material)    -   (B) Good (Slightly suffering from perceived see-through        property, but practically acceptable as anti-see-through fabric)    -   (C) Practically acceptable (practically useful for common uses)    -   (D) Poor (Transparency strongly perceived, and unacceptable as        fabric for underwear).

(12) Overall Evaluation of Cloth

Overall quality of cloth was evaluated according to the followingcriteria:

-   -   (A) Ranked as either (A) or (B) for all four items of softness,        dyeing quality, water absorption capacity, and anti-see-through        property of cloth. Ranked as (A) at least for two items.    -   (B) Ranked as (C) for one or less of the four items of softness,        dyeing quality, water absorption capacity, and anti-see-through        property of cloth. Ranked as (D) for none of them.    -   (C) Ranked as (C) for two or more of the four items of softness,        dyeing quality, water absorption capacity, and anti-see-through        property of cloth, although ranked as (D) for none of them.    -   (D) Ranked as (D) for one or more of the four items of softness,        dyeing quality, water absorption capacity, and anti-see-through        property of cloth.

Example 1

A NYLON 66 material with a 98% sulfuric acid relative viscosity of 2.63is melted at 285° C., supplied to a melt-spinning pack, and dischargedfrom an spinneret provided with 98 circular holes. The single yarns arepassed through a steam blow-out zone where steam is blown out toward thespinning spinneret face at a pressure of 0.25 kPa, then passed through astand-alone, outward blow type circular cooling apparatus provided witha cooling air supply portion that is located on the downstream side ofthe steam blow-out zone, has a cooling start distance of 30 mm, and hasa vertical length of 300 mm, and solidified as they are cooled bycooling air at 20° C. supplied radially outward at a flow speed of 40m/min. Subsequently, an emulsion finishing oil was supplied at aposition 500 mm from the spinneret face by a circular finishing oilsupply apparatus having a disk-like guide portion that is in contactwith the single yarns at its outer circumferential portion and alsohaving a circular finishing oil-discharge slit that is located directlyabove the guide portion and along the outer circumference of the guide,and the yarns are subjected to second-stage lubrication and bundled by abundle-guide type finishing oil supply apparatus. They are taken up at4,000 m/min while being interlaced, and then drawn at a draw ratio of1.10, and wound into a package at 4,200 m/min under relaxing conditionsto provide NYLON 66 fiber of 40 dtex/98 filaments and 45% elongationpercentage. The resulting raw yarn and cloth were subjected tocharacteristics evaluation. Results are given in Table 1. In Tables,NYLON 66 is abbreviated as N66.

Example 2

Except that a NYLON 6 material with a 98% sulfuric acid relativeviscosity of 2.63 was melted at 255° C., and fed to a melt-spinningpack, the same spinning procedure as in Example 1 was carried out toprovide NYLON 6 fiber of 40 dtex/98 filaments. The resulting raw yarnand cloth were subjected to characteristics evaluation. Results aregiven in Table 1. In Tables, NYLON 6 is abbreviated as N6.

Example 3

Except for using an spinneret provided with 268 circular holes, the samespinning procedure as in Example 1 was carried out to provide NYLON 66fiber of 40 dtex/268 filaments. The resulting raw yarn and cloth weresubjected to characteristics evaluation. Results are given in Table 1.

Example 4

Except for using an spinneret provided with 82 circular holes, the samespinning procedure as in Example 1 was carried out to provide NYLON 66fiber of 40 dtex/82 filaments. The resulting raw yarn and cloth weresubjected to characteristics evaluation. Results are given in Table 1.

Example 5

Except that the cooling air blow-out portion of the outward blow typecircular cooling apparatus installed on the downstream side of the steamblow-out zone under the spinneret had a vertical length of 100 mm andthat a finishing oil was supplied by the circular finishing oil supplyapparatus at a position 300 mm below the spinneret, the same spinningprocedure as in Example 1 was carried out to provide NYLON 66 fiber of40 dtex/98 filaments. The resulting raw yarn and cloth were subjected tocharacteristics evaluation. Results are given in Table 1.

Example 6

Except that a NYLON 66 material with a 98% sulfuric acid relativeviscosity of 2.63 was melted at 275° C., the same spinning procedure asin Example 1 was carried out to provide NYLON 66 fiber of 40 dtex/98filaments. The resulting raw yarn and cloth were subjected tocharacteristics evaluation. Results are given in Table 1.

TABLE 1 Item Unit Example 1 Example 2 Example 3 Example 4 Example 5Example 6 Total fineness Dtex 40 40 40 40 40 40 Filament number — 98 98268 82 98 98 Single yarn fineness Dtex 0.41 0.41 0.15 0.49 0.41 0.41Cross section shape — circular circular circular circular circularcircular Polymer — N66 N6 N66 N66 N66 N66 Cooling apparatus — outwardblow outward blow outward blow outward blow outward blow outward blowtype circular type circular type circular type circular type circulartype circular cooling cooling cooling cooling cooling cooling apparatusapparatus apparatus apparatus apparatus apparatus Polymer temperature °C. 285° C. 255° C. 285° C. 285° C. 285° C. 275° C. Spinneret-cooling Mm30 mm 30 mm 30 mm 30 mm 30 mm 30 mm apparatus distance Cooling air speedm/min 40 m/min 40 m/min 40 m/min 40 m/min 40 m/min 40 m/min Cooling airsupply length Mm 300 mm 300 mm 300 mm 300 mm 100 mm 300 mm The take-upspeed m/min 4000 4000 4000 4000 4000 4000 Draw ratio — 1.10 1.10 1.101.10 1.10 1.10 Finishing oil supply — circular circular circularcircular circular circular apparatus 1 finishing finishing finishingfinishing finishing finishing oil supply oil supply oil supply oilsupply oil supply oil supply apparatus apparatus apparatus apparatusapparatus apparatus Finishing oil supply — bundle-guide bundle-guidebundle-guide bundle-guide bundle-guide bundle-guide apparatus 2 typefinishing type finishing type finishing type finishing type finishingtype finishing oil supply oil supply oil supply oil supply oil supplyoil supply apparatus apparatus apparatus apparatus apparatus apparatusUster unevenness % 0.49 0.80 0.98 0.39 0.97 0.54 Average number offuzzes /12,000 m 0.0 0.0 0.8 0.0 0.2 0.9 Orientation parameter ratio —1.26 1.32 1.66 1.14 1.24 1.29 Stress at 15% elongation gf/dtex 1.30 1.351.70 1.21 1.32 1.29 (N/dtex) (12.7 × 10⁻³) (13.2 × 10⁻³) (16.7 × 10⁻³)(11.9 × 10⁻³) (12.9 × 10⁻³) (12.6 × 10⁻³) Softness of cloth (A) to (D)(A) (B) (A) (B) (A) (A) Dyeing quality of cloth (A) to (D) (A) (A) (C)(A) (C) (C) Water absorption capacity (A) to (D) (B) (B) (A) (C) (B) (B)of cloth Anti-see-through property (A) to (D) (B) (B) (A) (C) (B) (B) ofcloth Overall evaluation of cloth (A) to (D) (A) (B) (B) (c) (B) (B)

Example 7

Except that an spinneret provided with 42 circular holes was used andthat the fineness was 17 dtex, the same spinning procedure as in Example1 was carried out to provide NYLON 66 fiber of 17 dtex/42 filaments. Theresulting raw yarn and cloth were subjected to characteristicsevaluation. Results are given in Table 2.

Example 8

Except that an spinneret provided with 680 circular holes was used andthat the fineness was 280 dtex, the same spinning procedure as inExample 1 was carried out to provide NYLON 66 fiber of 280 dtex/680filaments. The resulting raw yarn and cloth were subjected tocharacteristics evaluation. Results are given in Table 2.

Example 9

Except that an spinneret provided with 32 circular holes was used andthat the fineness was 15 dtex, the same spinning procedure as in Example1 was carried out to provide NYLON 66 fiber of 15 dtex/32 filaments. Theresulting raw yarn and cloth were subjected to characteristicsevaluation. Results are given in Table 2.

Example 10

Except that a NYLON 6 material with a 98% sulfuric acid relativeviscosity of 2.63 was melted at 255° C., fed to a melt-spinning pack,and discharged from an spinneret provided with 98 discharge holes eachhaving a slit with a trilobal cross section as shown in FIG. 2, the samespinning procedure as in Example 1 was carried out to provide NYLON 6fiber of 40 dtex/98 filaments having a trilobal cross section. Theresulting raw yarn and cloth were subjected to characteristicsevaluation. Results are given in Table 2.

Example 11

Except for using a 98-hole spinneret provided with 49 discharge holeseach having a hexalobal cross section as shown in FIG. 3 and the samenumber of coexisting circular holes, the same spinning procedure as inExample 10 was carried out to provide NYLON 6 fiber of 40 dtex/98filaments in which hexalobal and circular cross sections coexist. Theresulting raw yarn and cloth were subjected to characteristicsevaluation. Results are given in Table 2.

TABLE 2 Item Unit Example 7 Example 8 Example 9 Example 10 Example 1Total fineness dtex 17 280 15 40 40 Filament number — 42 680 32 98 98Single yarn fineness dtex 0.40 0.41 0.47 0.41 circular 0.39/ hexalobal0.42 Cross section shape — circular circular circular trilobal circular/hexalobal combined Polymer — N66 N66 N66 N6 N6 Cooling apparatus —outward blow outward blow outward blow outward blow outward blow typecircular type circular type circular type circular type circular coolingcooling cooling cooling cooling apparatus apparatus apparatus apparatusapparatus Polymer temperature ° C. 285° C. 285° C. 285° C. 255° C. 255°C. Spinneret-cooling mm 30 mm 30 mm 30 mm 30 mm 30 mm apparatus distanceCooling air speed m/min 40 m/min 40 m/min 40 m/min 40 m/min 40 m/minCooling air supply length mm 300 mm 300 mm 300 mm 300 mm 300 mm Thetake-up speed m/min 4000 4000 4000 4000 4000 Draw ratio — 1.10 1.10 1.101.10 1.10 Finishing oil supply — circular circular circular circularcircular apparatus 1 finishing finishing finishing finishing finishingoil supply oil supply oil supply oil supply oil supply apparatusapparatus apparatus apparatus apparatus Finishing oil supply —bundle-guide bundle-guide bundle-guide bundle-guide bundle-guideapparatus 2 type finishing type finishing type finishing type finishingtype finishing oil supply oil supply oil supply oil supply oil supplyapparatus apparatus apparatus apparatus apparatus Uster unevenness %0.47 0.88 0.42 0.91 0.85 Average number of fuzzes /12,000 m 0.0 0.8 0.00.3 0.0 Orientation parameter ratio — 1.26 1.20 1.31 — 1.33 (circularcross section) Stress at 15% elongation gf/dtex 1.25 1.30 1.31 1.50 1.41(N/dtex) (12.3 × 10⁻³) (12.7 × 10⁻³) (12.8 × 10⁻³) (14.7 × 10⁻³) (13.8 ×1010⁻³) Softness of cloth (A) to (D) (B) (A) (B) (B) (B) Dyeing qualityof cloth (A) to (D) (B) (C) (A) (C) (B) Water absorption capacity (A) to(D) (C) (B) (B) (A) (A) of cloth Anti-see-through property (A) to (D)(B) (B) (C) (A) (A) of cloth Overall evaluation of cloth (A) to (D) (B)(B) (B) (B) (A)

Example 12

Except that the yarns were interlaced first, taken up at 3,000 m/min,drawn at a draw ratio of 1.50, and wound up at 4,300 m/min underrelaxing conditions, the same spinning procedure as in Example 1 wascarried out to provide NYLON 66 fiber of 40 dtex/98 filaments. Theresulting raw yarn and cloth were subjected to characteristicsevaluation. Results are given in Table 3.

Example 13

Except for passing the yarns through a stand-alone, inward blow typecircular cooling apparatus provided with a cooling air supply portionwith a vertical length of 300 mm instead of an outward blow typecircular cooling apparatus, the same spinning procedure as in Example 1was carried out to provide NYLON 66 fiber of 40 dtex/98 filaments. Theresulting raw yarn and cloth were subjected to characteristicsevaluation. Results are given in Table 3.

Example 14

Except that the cooling start distance was 20 mm, the same spinningprocedure as in Example 1 was carried out to provide NYLON 66 fiber of40 dtex/98 filaments. The resulting raw yarn and cloth were subjected tocharacteristics evaluation. Results are given in Table 3.

Example 15

Except that the cooling start distance was 40 mm, the same spinningprocedure as in Example 1 was carried out to provide NYLON 66 fiber of40 dtex/98 filaments. The resulting raw yarn and cloth were subjected tocharacteristics evaluation. Results are given in Table 3.

Example 16

Except that the cooling start distance was 10 mm, the same spinningprocedure as in Example 1 was carried out to provide NYLON 66 fiber of40 dtex/98 filaments. The resulting raw yarn and cloth were subjected tocharacteristics evaluation. Results are given in Table 3.

TABLE 3 Item Unit Example 12 Example 13 Example 14 Example 15 Example 16Total fineness dtex 40 40 40 40 40 Filament number — 98 98 98 98 98Single yarn fineness dtex 0.41 0.41 0.41 0.41 0.41 Cross section shape —circular circular circular circular circular Polymer — N66 N66 N66 N66N66 Cooling apparatus — outward blow inward blow outward blow outwardblow outward blow type circular type circular type circular typecircular type circular cooling cooling cooling cooling cooling apparatusapparatus apparatus apparatus apparatus Polymer temperature ° C. 285° C.285° C. 285° C. 285° C. 285° C. Spinneret-cooling mm 30 mm 30 mm 20 mm40 mm 10 mm apparatus distance Cooling air speed m/min 40 m/min 40 m/min40 m/min 40 m/min 40 m/min Cooling air supply length mm 300 mm 300 mm300 mm 300 mm 300 mm The take-up speed m/min 3000 4000 4000 4000 4000Draw ratio — 1.50 1.10 1.10 1.10 1.10 Finishing oil supply — circularcircular circular circular circular apparatus 1 finishing finishingfinishing finishing finishing oil supply oil supply oil supply oilsupply oil supply apparatus apparatus apparatus apparatus apparatusFinishing oil supply — bundle-guide bundle-guide bundle-guidebundle-guide bundle-guide apparatus 2 type finishing type finishing typefinishing type finishing type finishing oil supply oil supply oil supplyoil supply oil supply apparatus apparatus apparatus apparatus apparatusUster unevenness % 0.45 0.56 0.46 0.56 0.45 Average number of fuzzes/12,000 m 0.9 0.5 0.1 0.0 0.6 Orientation parameter ratio — 1.12 1.191.31 1.15 1.34 Stress at 15% elongation gf/dtex 1.50 1.31 1.31 1.28 1.33(N/dtex) (14.7 × 10⁻³) (12.8 × 10⁻³) (12.8 × 10⁻³) (12.5 × 10⁻³) (13.0 ×10⁻³) Softness of cloth (A) to (D) (B) (A) (A) (A) (A) Dyeing quality ofcloth (A) to (D) (B) (B) (B) (A) (C) Water absorption capacity (A) to(D) (B) (B) (B) (B) (B) of cloth Anti-see-through property (A) to (D)(C) (B) (A) (B) (A) of cloth Overall evaluation of cloth (A) to (D) (B)(B) (A) (A) (B)

Example 17

Except that the cooling start distance was 60 mm, the same spinningprocedure as in Example 1 was carried out to provide NYLON 66 fiber of40 dtex/98 filaments. The resulting raw yarn and cloth were subjected tocharacteristics evaluation. Results are given in Table 4.

Example 18

Except that the flow speed of the cooling air at 20° C. sent radiallyoutward from the outward blow type circular cooling apparatus was 27m/min, the same spinning procedure as in Example 1 was carried out toprovide NYLON 66 fiber of 40 dtex/98 filaments. The resulting raw yarnand cloth were subjected to characteristics evaluation. Results aregiven in Table 4.

Example 19

Except that the flow speed of the cooling air at 20° C. sent radiallyoutward from the outward blow type circular cooling apparatus was 49m/min, the same spinning procedure as in Example 1 was carried out toprovide NYLON 66 fiber of 40 dtex/98 filaments. The resulting raw yarnand cloth were subjected to characteristics evaluation. Results aregiven in Table 4.

Example 20

Except that the flow speed of the cooling air at 20° C. sent radiallyoutward from the outward blow type circular cooling apparatus was 17m/min, the same spinning procedure as in Example 1 was carried out toprovide NYLON 66 fiber of 40 dtex/98 filaments. The resulting raw yarnand cloth were subjected to characteristics evaluation. Results aregiven in Table 4.

Example 21

Except that the flow speed of the cooling air at 20° C. sent radiallyoutward from the outward blow type circular cooling apparatus was 58m/min, the same spinning procedure as in Example 1 was carried out toprovide NYLON 66 fiber of 40 dtex/98 filaments. The resulting raw yarnand cloth were subjected to characteristics evaluation. Results aregiven in Table 4.

TABLE 4 Item Unit Example 17 Example 18 Example 19 Example 20 Example 21Total fineness dtex 40 40 40 40 40 Filament number — 98 98 98 98 98Single yarn fineness dtex 0.41 0.41 0.41 0.41 0.41 Cross section shape —circular circular circular circular circular Polymer — N66 N66 N66 N66N66 Cooling apparatus — outward blow outward blow outward blow outwardblow outward blow type circular type circular type circular typecircular type circular cooling cooling cooling cooling cooling apparatusapparatus apparatus apparatus apparatus Polymer temperature ° C. 285° C.285° C. 285° C. 285° C. 285° C. Spinneret-cooling apparatus mm 60 mm 30mm 30 mm 30 mm 30 mm distance Cooling air speed m/min 40 m/min 27 m/min49 m/min 17 m/min 58 m/min Cooling air supply length mm 300 mm 300 mm300 mm 300 mm 300 mm The take-up speed m/min 4000 4000 4000 4000 4000Draw ratio — 1.10 1.10 1.10 1.10 1.10 Finishing oil supply — circularcircular circular circular circular apparatus 1 finishing finishingfinishing finishing finishing oil supply oil supply oil supply oilsupply oil supply apparatus apparatus apparatus apparatus apparatusFinishing oil supply — bundle-guide bundle-guide bundle-guidebundle-guide bundle-guide apparatus 2 type finishing type finishing typefinishing type finishing type finishing oil supply oil supply oil supplyoil supply oil supply apparatus apparatus apparatus apparatus apparatusUster unevenness % 0.97 0.70 0.65 0.99 0.89 Average number of fuzzes/12,000 m 0.1 0.0 0.2 0.4 0.7 Orientation parameter ratio — 1.13 1.191.27 1.15 1.30 Stress at 15% elongation gf/dtex 1.25 1.32 1.31 1.36 1.33(N/dtex) (12.2 × 10⁻³) (12.9 × 10⁻³) (12.8 × 10⁻³) (13.3 × 10⁻³) (13.0 ×10⁻³) Softness of cloth (A) to (D) (A) (A) (A) (A) (A) Dyeing quality ofcloth (A) to (D) (C) (A) (B) (C) (C) Water absorption capacity (A) to(D) (B) (B) (B) (B) (B) of cloth Anti-see-through property (A) to (D)(C) (B) (A) (C) (A) of cloth Overall evaluation of cloth (A) to (D) (C)(A) (A) (C) (B)

Comparative Example 1

Except that yarns were discharged from an spinneret provided with 160circular holes and that the fineness was 15 dtex, the same spinningprocedure as in Example 1 was carried out to provide NYLON 66 fiber of15 dtex/160 filaments. The resulting raw yarn and cloth were subjectedto characteristics evaluation. Results are given in Table 5.

Comparative Example 2

Except that the fineness was 56 dtex, the same spinning procedure as inExample 1 was carried out to provide NYLON 66 fiber of 56 dtex/98filaments. The resulting raw yarn and cloth were subjected tocharacteristics evaluation. Results are given in Table 5.

Comparative Example 3

Except that a disk-like guide that did not have a finishingoil-discharging circular slit was provided at a position 500 mm from thespinneret face located vertically below the outward blow type circularcooling apparatus and that finishing oil supply was not performed forthe single yarns that were maintained in contact with the disk-likeguide, the same spinning procedure as in Example 1 was carried out toprovide NYLON 66 fiber of 40 dtex/98 filaments. The resulting raw yarnand cloth were subjected to characteristics evaluation. Results aregiven in Table 5.

Comparative Example 4

Except that polyethylene terephthalate resin was melted at 290° C. andthen fed to a melt-spinning pack, the same spinning procedure as inExample 1 was carried out to provide polyethylene terephthalate fiber of40 dtex/98 filaments. The resulting raw yarn and cloth were subjected tocharacteristics evaluation. Results are given in Table 5.

Comparative Example 5

Except that a unidirectional type uniflow chimney was used as thecooling apparatus and that the yarns were bundled and lubricated by afinishing oil supply guide, the same spinning procedure as in Example 1was carried out to provide NYLON 66 fiber of 40 dtex/98 filaments. Theresulting raw yarn and cloth were subjected to characteristicsevaluation. Results are given in Table 5.

Comparative Example 6

Except that a finishing oil was supplied by a circular finishing oilsupply apparatus and then the yarns were bundled without being subjectedto a second-stage finishing oil supply, the same spinning procedure asin Example 1 was carried out to provide NYLON 66 fiber of 40 dtex/98filaments. The resulting raw yarn and cloth were subjected tocharacteristics evaluation. Results are given in Table 5.

TABLE 5 Comparative Comparative Comparative Comparative ComparativeComparative Item Unit Example 1 Example 2 Example 3 Example 4 Example 5Example 6 Total fineness Dtex 15 56 40 40 40 40 Filament number — 160 9898 98 98 98 Single yarn fineness Dtex 0.09 0.57 0.41 0.41 0.41 0.41Cross section shape — circular circular circular circular circularcircular Polymer — N66 N66 N66 PET N66 N66 Cooling apparatus — outwardblow outward blow outward blow outward blow uniflow outward blow typecircular type circular type circular type circular chimney type circularcooling cooling cooling cooling cooling apparatus apparatus apparatusapparatus apparatus Polymer temperature ° C. 285° C. 285° C. 285° C.290° C. 285° C. 285° C. Spinneret-cooling Mm 30 mm 30 mm 30 mm 30 mm 30mm 30 mm apparatus distance Cooling air speed m/min 40 m/min 40 m/min 40m/min 40 m/min 40 m/min 40 m/min Cooling air supply length Mm 300 mm 300mm 300 mm 300 mm 300 mm 300 mm The take-up speed m/min 4000 4000 40004000 4000 4000 Draw ratio — 1.10 1.10 1.10 1.10 1.10 1.10 Finishing oilsupply — circular circular contact with circular — circular apparatus 1finishing finishing circular finishing finishing oil supply oil supplywithout oil supply oil supply apparatus apparatus finishing oilapparatus apparatus supply Finishing oil supply — bundle-guidebundle-guide bundle-guide bundle-guide bundle-guide yarns bundledapparatus 2 type finishing type finishing type finishing type finishingtype finishing without oil supply oil supply oil supply oil supply oilsupply finishing apparatus apparatus apparatus apparatus apparatus oilsupply Uster unevenness % 1.20 0.38 0.88 0.31 3.10 1.11 Average numberof fuzzes /12,000 m 2.0 0.0 1.3 0.0 7.2 1.2 Orientation parameter ratio— 1.90 1.07 1.24 1.85 1.01 1.25 Stress at 15% elongation gf/dtex 1.501.27 1.31 1.45 1.81 1.30 (N/dtex) (14.7 × 10⁻³) (12.4 × 10⁻³) (12.8 ×10⁻³) (14.2 × 10⁻³) (17.7 × 10⁻³) (12.7 × 10⁻³) Softness of cloth (A) to(D) (A) (C) (A) (D) (A) (A) Dyeing quality of cloth (A) to (D) (D) (A)(D) (B) (D) (D) Water absorption capacity (A) to (D) (B) (C) (B) (D) (B)(B) of cloth Anti-see-through property (A) to (D) (A) (D) (B) (A) (D)(B) of cloth Overall evaluation of cloth (A) to (D) (D) (D) (D) (D) (D)(D)

1-10. (canceled)
 11. Ultrafine polyamide fiber comprising polyamidefiber with a single yarn fineness of 0.10 dtex or more and 0.50 dtex orless and an average number of fuzzes of 1.0 or less per 12,000 m of afilament in a length direction.
 12. The ultrafine polyamide fiber asdefined in claim 11, wherein Uster unevenness in a filament in a lengthdirection is 1.0% or less.
 13. The ultrafine polyamide fiber as definedin claim 11, having a total fineness of 15 to 300 dtex and containing 30or more filaments.
 14. The ultrafine polyamide fiber as defined claim12, having a total fineness of 15 to 300 dtex and containing 30 or morefilaments.
 15. The ultrafine polyamide fiber as defined in claim 11,wherein filaments have a modified cross section.
 16. The ultrafinepolyamide fiber as defined in claim 12, wherein filaments have amodified cross section.
 17. The ultrafine polyamide fiber as defined inclaim 13, wherein filaments have a modified cross section.
 18. Theultrafine polyamide fiber as defined in claim 14, wherein filaments havea modified cross section.
 19. The ultrafine polyamide fiber as definedin claim 11, wherein the single yarns contained in the ultrafinepolyamide fiber have a circular filament cross section, orientationparameters of the single yarns with a circular cross section are suchthat a ratio of an orientation parameter of a surface portion of thesingle yarn to an orientation parameter of a central portion of thesingle yarn is 1.10 or more.
 20. The ultrafine polyamide fiber asdefined in claim 12, wherein the single yarns contained in the ultrafinepolyamide fiber have a circular filament cross section, orientationparameters of the single yarns with a circular cross section are suchthat a ratio of an orientation parameter of a surface portion of thesingle yarn to an orientation parameter of a central portion of thesingle yarn is 1.10 or more.
 21. The ultrafine polyamide fiber asdefined in claim 13, wherein the single yarns contained in the ultrafinepolyamide fiber have a circular filament cross section, orientationparameters of the single yarns with a circular cross section are suchthat a ratio of an orientation parameter of a surface portion of thesingle yarn to an orientation parameter of a central portion of thesingle yarn is 1.10 or more.
 22. The ultrafine polyamide fiber asdefined in claim 14, wherein the single yarns contained in the ultrafinepolyamide fiber have a circular filament cross section, orientationparameters of the single yarns with a circular cross section are suchthat a ratio of an orientation parameter of a surface portion of thesingle yarn to an orientation parameter of a central portion of thesingle yarn is 1.10 or more.
 23. A melt-spinning method for ultrafinepolyamide fiber having a single yarn fineness of 0.10 dtex or more and0.50 dtex or less and having an average of 1.0 or less fuzzes per 12,000m in a length direction, wherein melt-spun yarns discharged from aspinning spinneret provided with discharge holes arrangedcircumferentially in the outer circumferential portion of the spinningspinneret are cooled by a cooling apparatus located below a centralportion of the spinning spinneret and cool the melt-spun yarns byapplying cooling air from either inside or outside of the melt-spunyarns discharged from the discharge holes, a finishing oil is suppliedby a circular finishing oil supply apparatus having a disk-like guideportion located vertically below the cooling apparatus and that is incontact with the single yarns at its outer circumferential portion andalso having a circular finishing oil-discharging slit located directlyabove the guide portion and arranged along the outer circumference ofthe guide and, subsequently, the yarns are bundled by a bundle-guidetype finishing oil supply apparatus while receiving a second-stagefinishing oil supply.
 24. The method as defined in claim 23, wherein thecooling apparatus cools the melt-spun yarns by supplying cooling airfrom inside of the melt-spun yarns discharged from the discharge holes.25. The method as defined in claim 23, wherein the cooling apparatussatisfies: (1) distance (L) from a face of the spinning spinneret to acooling start position of the cooling apparatus is as follows: 10mm≦L≦70 mm, and (2) cooling air provided at the cooling start positionhas a flow speed of 15 to 60 m/min.
 26. The method as defined in claim24, wherein the cooling apparatus satisfies: (1) distance (L) from aface of the spinning spinneret to a cooling start position of thecooling apparatus is as follows: 10 mm≦L≦70 mm, and (2) cooling airprovided at the cooling start position has a flow speed of 15 to 60m/min.
 27. A melting spinning apparatus that produces ultrafinepolyamide fiber having a single yarn fineness of 0.10 dtex or more and0.50 dtex or less and having an average of 1.0 or less fuzzes per 12,000m in a length direction, comprises: a spinning spinneret provided withdischarge holes arranged circumferentially in an outer circumferentialportion of the spinning spinneret, and a cooling apparatus located belowa central portion of the spinning spinneret and cools the melt-spunyarns by applying cooling air from inside or outside of the melt-spunyarns discharged from the discharge holes, and a circular finishing oilsupply apparatus having a disk-like guide portion located verticallybelow the cooling apparatus and in contact with the single yarns at anouter-circumferential portion, a circular finishing oil-discharging slitlocated directly above the guide portion and arranged along an outercircumference of the guide, and a bundle-guide type finishing oil supplyapparatus located thereunder and intended to bundle the yarns whileperforming a second-stage finishing oil supply.
 28. The melt-spinningapparatus for ultrafine polyamide fiber as defined in claim 27, whereinthe cooling apparatus cools the melt-spun yarns by supplying cooling airfrom inside of the melt-spun yarns discharged from the discharge holes.